Abstract:

A gas turbine engine control system comprises a data acquisition and
analysis system for receiving a signal from a combustion dynamics sensor
and providing an output signal and a combustion dynamics control system
for controlling combustion dynamics based on the output signal. The
control system is associated with a purge-air flow and comprises an
acoustic driver, or a flow-manipulating device, or both to perturb the
purge-air flow entering the combustor can for controlling combustion
dynamics.

Claims:

1. A gas turbine engine control system, comprising:a data acquisition and
analysis system for receiving a signal from a combustion dynamics sensor
and providing an output signal; anda combustion dynamics control system
for controlling combustion dynamics based on the output signal, the
control system is associated with a purge-air flow and comprises an
acoustic driver, or a flow-manipulating device, or both to perturb the
purge-air flow entering a combustor can for controlling combustion
dynamics.

2. The system of claim 1, wherein the control system controls combustion
dynamics if the output signal is indicative of combustion dynamics.

3. The system of claim 1, wherein the flow-manipulating device comprises a
perturbation valve in a path of the purge-air flow to perturb the
purge-air flow.

4. The system of claim 1, wherein the acoustic driver is configured to
send an acoustic wave in a path of the purge-air flow to perturb the
purge-air flow.

5. The system of claim 1, wherein the purge-air flow is perturbed to cause
fluctuations in equivalence ratio and flow rate for mitigating combustion
dynamics.

6. The system of claim 1, wherein the control system further comprises a
dedicated flow path for delivering a flow into the combustor can and an
additional acoustic driver.

7. The system of claim 6, wherein the control system further comprises a
controller to control the acoustic drivers, the flow-manipulating device,
and the flow delivered through the dedicated flow path.

8. The system of claim 6, wherein a vortex phenomenon in the combustor can
is perturbed by the additional acoustic driver, the flow delivered
through the dedicated flow path, or a combination of both for controlling
combustion dynamics.

9. The system of claim 8, wherein the additional acoustic driver is
configured to send an acoustic wave into the combustor can to perturb the
vortex phenomenon.

10. The system of claim 8, wherein the flow delivered through the
dedicated flow path comprises fuel, air, or a mixture of fuel and air.

11. The system of claim 8, wherein the vortex phenomenon is perturbed to
mitigate combustion dynamics.

12. The system of claim 8, wherein the vortex phenomenon comprises vortex
shedding, flame-vortex interaction, or a combination thereof.

13. The system of claim 1, wherein the combustion dynamics sensor is
associated with the combustor can.

14. The system of claim 13, wherein the combustion dynamics sensor
comprises a dynamic pressure sensor or a flame sensor.

15. A gas turbine engine control method, comprising:receiving a signal
from a combustion dynamics sensor; andcontrolling combustion dynamics
based on the received signal by perturbing a purge-air flow entering a
combustor can using acoustic signals, flow-manipulation, or a combination
thereof.

16. The method of claim 15, wherein controlling comprises controlling
combustion dynamics if the received signal is indicative of combustion
dynamics.

17. The method of claim 16, wherein using flow-manipulation comprises
inducing perturbation in a path of the purge-air flow to perturb the
purge-air flow.

19. The method of claim 15, wherein controlling combustion dynamics
further comprises controlling combustion dynamics based on the received
signal by perturbing a vortex phenomenon in the combustor can using the
acoustic signals, a dedicated flow into a combustor can, or a combination
thereof.

20. The method of claim 19, wherein the dedicated flow comprises fuel,
air, or a mixture of fuel and air.

23. The method of claim 15, wherein the combustion dynamics sensor is
associated with a combustor can.

24. The method of claim 15, wherein the combustion dynamics sensor
comprises a dynamic pressure sensor or a flame sensor.

25. A system for a gas turbine engine, comprising:a data acquisition and
analysis system for receiving a signal from a combustion dynamics sensor
and providing an output signal; anda combustion dynamics control system
for controlling combustion dynamics based on the output signal, the
control system comprising a controller and at least one of an acoustic
driver, a flow-manipulating device, and a dedicated flow path for
delivering a flow into a combustor can to perturb a purge-air flow
entering the combustor can, perturb a vortex phenomenon in the combustor
can, or both for controlling combustion dynamics.

26. A gas turbine engine control method, comprising:receiving a signal
from a combustion dynamics sensor; andcontrolling combustion dynamics
based on the received signal by perturbing a purge-air flow entering a
combustor can, a vortex phenomenon in the combustor can, or both using
acoustic signals, flow-manipulation, a dedicated flow into a combustor
can, or a combination thereof.

Description:

BACKGROUND

[0001]The invention relates generally to methods for controlling the
operation of gas turbine engines and, more particularly, to a method of
controlling combustion dynamics in gas turbines.

[0002]Gas turbines engines include a compressor, a combustor, and a
turbine coupled to the compressor. The combustor can include a plurality
of combustor cans. Compressed air and fuel are delivered to the combustor
cans to produce high-velocity and high-pressure combustion gases. These
combustion gases are discharged to the turbine. The turbine extracts
energy from the combustion gases for producing power that can be used in
several ways such as, for example, to power the compressor, to power an
electrical generator, or to power an aircraft.

[0003]Gas turbine engines operate under different load conditions that
necessitate varying combustion operating conditions for the combustors to
meet desired performance. Under some conditions, combustion phenomenon
can interact with natural modes of combustors, establishing a feedback
cycle. This leads to high-amplitude pressure fluctuations or
perturbations. These pressure perturbations are referred to as combustion
dynamics. Combustion dynamics are capable of restricting the operating
conditions of the gas turbine and can also cause hardware damage or
unscheduled shutdown.

[0004]Combustion dynamics is an issue faced by all types of combustors.
Due to the design, combustion dynamics are relatively more severe for
modern pre-mixed combustion systems that were developed in order to
achieve reduced emissions. It would therefore be desirable to provide a
method for controlling combustion dynamics in gas turbine engines.

BRIEF DESCRIPTION

[0005]In accordance with one embodiment disclosed herein, a gas turbine
engine control system comprises a data acquisition and analysis system
for receiving a signal from a combustion dynamics sensor and providing an
output signal and a combustion dynamics control system for controlling
combustion dynamics based on the output signal. The control system is
associated with a purge-air flow and comprises an acoustic driver, or a
flow-manipulating device, or both to perturb the purge-air flow entering
the combustor can for controlling combustion dynamics.

[0006]In accordance with another embodiment disclosed herein, a gas
turbine engine control method comprises receiving a signal from a
combustion dynamics sensor and controlling combustion dynamics based on
the received signal by perturbing a purge-air flow entering a combustor
can using acoustic signals, flow-manipulation, or a combination thereof.

[0007]In accordance with another embodiment disclosed herein, a system for
a gas turbine engine comprises a data acquisition and analysis system for
receiving a signal from a combustion dynamics sensor and providing an
output signal and a combustion dynamics control system for controlling
combustion dynamics based on the output signal. The control system
comprises a controller and at least one of an acoustic driver, a
flow-manipulating device, and a dedicated flow path for delivering a flow
into a combustor can to perturb a purge-air flow entering the combustor
can, perturb a vortex phenomenon in the combustor can, or both for
controlling combustion dynamics.

[0008]In accordance with another embodiment disclosed herein, a gas
turbine engine control method comprises receiving a signal from a
combustion dynamics sensor and controlling combustion dynamics based on
the received signal by perturbing a purge-air flow entering a combustor
can, a vortex phenomenon in the combustor can, or both using acoustic
signals, flow-manipulation, a dedicated flow into a combustor can, or a
combination thereof.

DRAWINGS

[0009]These and other features, aspects, and advantages of the present
invention will become better understood when the following detailed
description is read with reference to the accompanying drawings in which
like characters represent like parts throughout the drawings, wherein:

[0013]FIG. 4 illustrates a functional block diagram of a gas turbine
engine control system in accordance with aspects disclosed herein.

[0014]FIG. 5 illustrates a block diagram of data acquisition and analysis
system in accordance with aspects disclosed herein.

[0015]FIG. 6 illustrates a block diagram of a gas turbine control method
in accordance with aspects disclosed herein.

DETAILED DESCRIPTION

[0016]Embodiments disclosed herein include a system and method for
controlling combustion dynamics in gas turbine engines. The system and
method control combustion dynamics in a combustor can by perturbing a
purge-air flow entering the combustor can, a vortex phenomenon in the
combustor can, or both. Acoustic signals, flow manipulation, dedicated
flow path, or a combination thereof are used to perturb purge-air flow
and vortex phenomenon. Although the system and method are described
herein in the context of a heavy duty gas turbine engine employed for
industrial application, the system and method are applicable to other
combustion engine systems utilized in various applications such as, but
not limited to, aircraft, marine, helicopter, and prime-mover
applications. As used herein, singular forms such as "a," "an," and "the"
include plural referents unless the context clearly dictates otherwise.

[0017]FIG. 1 illustrates an exemplary gas turbine engine 10. The gas
turbine engine 10 includes a multi-stage axial compressor 12, a multi-can
combustor 14, and a multi-stage turbine 16. Ambient air is drawn in by
the compressor 12 and compressed to higher pressure and temperature. The
compressed air is then supplied to the combustor 14. In the combustor 14,
the incoming compressed air is mixed with fuel and the fuel-air mixture
is combusted to produce high-pressure and high-temperature combustion
gases. These combustion gases are discharged to the turbine 16. The
turbine 16 extracts energy from the combustion gases. The energy
extracted from the turbine 16 can be for various purposes such as
generating electrical power, providing propulsive thrust, or providing
shaft power for marine or prime mover applications.

[0018]FIG. 2 is a schematic of a gas turbine combustor 14. The combustor
14 may be of annular, can, or can-annular type combustor. The combustor
14 can have different types of nozzles 16 depending on intended
application. Modern low-emission combustors typically employ a pre-mixer
nozzle in which fuel is injected in an air stream and mixed before
reaching a combustion chamber 18. A typical combustor 14 will have
multiple pre-mixer nozzle groups and different number of nozzles in each
group. This is required to achieve performance objectives under various
load conditions. The classification of various nozzle groups depends on
their intended purpose.

[0019]FIG. 3 illustrates a portion of the gas turbine combustion system 20
in respect to a single combustor can. The combustor system 20 includes a
combustor can 22 defining a combustion chamber 24 therein. The combustor
can 22 is generally annular in form and includes a liner 26. Fuel is
injected into the combustor can 22 through a nozzle 28. The system 20
also includes a burner tube 30, swirlers 32 having vanes, and a purge-air
supply line 34. The swirlers 32 promote counter-rotation to an airflow
provided to the combustor can 22. A vortex structure 36 is formed in the
combustion chamber 24 in proximity to flame surface 38 during the
operation of gas turbine. Vortex phenomena such as vortex shedding from
flame and flame-vortex interaction may be generated during the operation
of gas turbine.

[0020]FIG. 4 illustrates a block diagram of an embodiment of a gas turbine
engine control system 40. The control system 40 includes a data
acquisition and analysis system 42, a combustion dynamics sensor 44, and
a combustion dynamics control system 46. Although only one combustor can
48 is shown, the control system can be adapted to any number of combustor
cans. In one embodiment, each combustor can 48 is equipped with the
combustion dynamics sensor 44.

[0021]The combustion dynamics sensor 44 generates signals 50 representing
combustion dynamics. The sensor 44 can monitor either pressure
fluctuations or flame perturbations inside the combustor can. The sensor
44 can be a pressure sensor or a flame sensor such as an optical or
chemical sensor for measuring flame response. The signals 50 from the
sensor 44 are provided to the data acquisition and analysis system 42.

[0022]The data acquisition and analysis system 42 receives signals 50 from
the sensor 44 and processes them to provide an output signal 52 to the
combustion dynamics control system 46. Several signal processing
techniques can be used for processing the signals 50 received from the
combustor can to generate the output signal 52 that accurately represents
combustion dynamics. The output signal 52 will then be utilized by the
combustion dynamics control system for controlling combustion dynamics.

[0023]Fluctuations in equivalence ratio (fuel-air ratio) and velocity
(flow-rate) are the main factors responsible for causing combustion
dynamics. Vortex phenomena such as vortex shedding from flame and
flame-vortex interaction are also responsible for causing combustion
dynamics. The combustion dynamics control system 46 reduces combustion
dynamics by fluctuating or perturbing equivalence ratio, velocity, vortex
phenomena, or any combination thereof. It should be noted that the terms
"fluctuations", "perturbations", "oscillations" can be used
interchangeably in context of this application.

[0024]In one embodiment, the combustion dynamics control system 46
comprises a controller 54, acoustic drivers 56 and 58, a
flow-manipulating device 60, and a dedicated flow path 62. The acoustic
driver 56, the flow-manipulating device 60, or both are used to perturb a
purge-air or inert flow 64 entering the combustor can. The purge-air flow
64 can enter the combustion can 48 through diffusion passage (not shown),
oil cartridge (not shown), or other nozzle passages (not shown). The
acoustic driver 56 is configured to send acoustic energy or acoustic
waves 66 through the purge-air flow 64. Acoustic drivers may include
siren devices, speakers, or other similar equipment capable of generating
acoustic waves at a desired frequency. In one embodiment, the acoustic
driver 56 can be placed in the path 68 of the purge-air flow 64. The
acoustic signals 66 passing through the purge-air will generate
perturbations in purge-air flow.

[0025]A perturbation valve 70 can be used as the flow-manipulating device.
The perturbation valve 70 is placed in the path of the purge-air flow.
When activated, the perturbation valve 70 creates fluctuations in the
purge-air flow 64. In one embodiment, the perturbation valve is a fluidic
valve. Alternately, the perturbation valve can be a mechanical valve, an
electromechanical valve, or any other valve capable of generating
perturbations in the flow rate.

[0026]If the output signal 52 is indicative of combustion dynamics, the
controller 54 provides commands to perturb purge airflow 64. The
controller 54 activates the acoustic driver 56 or the perturbation valve
70 or both to perturb purge airflow 64. The perturbed purge-air flow 64
will in turn cause perturbations in equivalence ratio and velocity at
flame-base and propagates through the flame. Equivalence ratio and
velocity fluctuations modulate combustion in the combustor can 48 and
interaction of combustion with acoustic field, thereby mitigating
combustion dynamics.

[0027]The dedicated flow path 62 is used for delivering a flow 72 into the
combustor can 48. This flow 72 can include fuel, air, or a mixture of
fuel and air. The flow 72 from the dedicated flow path 62 enters the
combustor can 48 and perturbs vortex phenomena. In addition, an
additional acoustic driver 58 can be configured to send an acoustic wave
66 into the combustor can 48 to perturb the vortex phenomenon.

[0028]If the output signal 52 is indicative of combustion dynamics, the
controller 54 provides commands to perturb vortex phenomena. The
controller 54 can control the flow 72 being introduced into the combustor
can and/or can activate the acoustic driver 58 to perturb vortex
phenomena. Perturbations in vortex phenomena will disturb vortex
phenomena such as vortex shedding from flame and flame-vortex
interaction, thereby mitigating or eliminating combustion dynamics.

[0029]The controller 54 is in real time communication with the data
acquisition and analysis system 42. The controller 54 can control any of
the acoustic drivers 56 and 58, the flow-manipulating device 60, and the
flow 72 from the dedicated flow path 62 either alone or in various
combinations. For example, if an output signal 52 at a first instance is
indicative of combustion dynamics, the controller 54 can activate only
the acoustic driver 56 in the purge-air flow path 68 to send an acoustic
wave 66. There may be a change in combustion dynamics upon activation of
the acoustic driver 56. A subsequent output signal at second instance
from the data acquisition and analysis system 42 will indicate whether
the activation of the acoustic driver 56 reduced or eliminated combustion
dynamics. If there is no change in combustion dynamics or if there is an
increase in combustion dynamics, the controller 54 can tune the acoustic
driver 56 to send an acoustic wave at different frequency. An output
signal at third instance will indicate any effect on combustion dynamics.
This process can be repeated to reduce combustion dynamics.

[0030]Similarly, the controller 54 can activate the flow-manipulating
device 60 either alone or in combination with the acoustic driver 56 and
check for feedback from the output signal 52 after the activation. If the
feedback indicates reduction or elimination in combustion dynamics, the
controller 54 can deactivate the acoustic driver 56 and flow-manipulating
device 60 and normal operation is resumed.

[0031]If the control of the flow-manipulating device 60, the acoustic
driver 56, or combination of both does not provide any reduction in
combustion dynamics, then it can be interpreted that combustion dynamics
are not caused by fluctuations of the equivalence ratio or velocity.
Therefore, there is a possibility that vortex phenomena may be causing
combustion dynamics. The controller 54 may then activate the additional
acoustic driver 58. In addition, the controller 54 can also start the
flow 72 from the dedicated flow path 62. If the feedback from the data
acquisition and analysis system 42 indicates reduction or elimination in
combustion dynamics, the controller 54 can deactivate the acoustic driver
58 and stop the flow 72.

[0032]As discussed previously, the controller 54 can control any of the
acoustic drivers 56 and 58, the flow-manipulating device 60, and the flow
72 from the dedicated flow path 62 either alone or in various
combinations and also in different order. The controller 54 and the data
acquisition and analysis system 42 are in real-time communication.
Therefore, the controller 54 can try different control combinations to
reduce combustion dynamics in a relatively short time, much before
combustion dynamics lead to unwanted effects in operation of gas
turbines.

[0033]FIG. 5 illustrates a block diagram of an embodiment of a signal
processing technique 80 used by the data acquisition and analysis system.
In one embodiment, signals 82 from combustion dynamics sensor are passed
through an anti-aliasing filter 84 to ensure minimum distortion from high
frequency components. The signal is then processed through a band-pass
filter 86 in order to curtail frequency content of the signal to yield
data within a frequency band of interest. A determination of sampling
frequency is then made at block 88 according to Nyquist criterion that
states that a sampling frequency must be at least twice the maximum
frequency of interest. Similarly, a sampling window is selected in line
with required frequency resolution and energy leakage. The signal is then
supplied to a Fast Fourier Transform (FFT) analyzer 90 that converts a
time-domain signal to a frequency-domain signal. The frequency spectra
are averaged at block 92 over multiple instances (for example 64
instances) in order to obtain a more representative signal content that
is not influenced by transients in the system. The averaged spectra are
then evaluated and the peak frequency and its amplitude in various bands
are determined at block 94. This peak frequency and amplitude data forms
the output signal 96 that is provided to the controller.

[0034]FIG. 6 illustrates a block diagram of a gas turbine control method
100. At block 102, a signal is received from a combustion dynamics
sensor. The determination of whether the received signal is indicative of
combustion dynamics is made at block 104. If the signal is not indicative
of combustion dynamics, then the method proceeds to block 102. If the
signal is indicative of combustion dynamics, then the method proceeds to
block 106 for controlling combustion dynamics. Combustion dynamics can be
controlled either by perturbing purge-air flow entering a combustor can
at block 108 or by perturbing vortex phenomena a combustor can at block
110. Both purge-air flow and vortex phenomena can be perturbed to control
combustion dynamics.

[0035]Purge-air flow is perturbed by using acoustic signals,
flow-manipulation, or both. Vortex phenomenon in the combustor can is
perturbed by acoustic signals, a dedicated flow into a combustor can, or
both. After blocks 108 and 110, the method starts from the beginning and
the process is repeated until combustion dynamics are either eliminated
or mitigated to an accepted or tolerable level.

[0036]The gas turbine engine control system and method described above
thus provide a way to control combustion dynamics by perturbing purge-air
flow and perturbing vortex phenomena to control combustion dynamics. The
control system and method mitigate or eliminate combustion dynamics to
prevent any damage to gas turbines. The control system and method can be
integrated with existing gas turbine control systems.

[0037]It is to be understood that not necessarily all such objects or
advantages described above may be achieved in accordance with any
particular embodiment. Thus, for example, those skilled in the art will
recognize that the systems and techniques described herein may be
embodied or carried out in a manner that achieves or optimizes one
advantage or group of advantages as taught herein without necessarily
achieving other objects or advantages as may be taught or suggested
herein.

[0038]While only certain features of the invention have been illustrated
and described herein, many modifications and changes will occur to those
skilled in the art. It is, therefore, to be understood that the appended
claims are intended to cover all such modifications and changes as fall
within the true spirit of the invention.